The sequence specificity of two resolved correndonucleases specific for the UV photoproducts, thymine-thymine, thymine-cytosine and cytosine-cytosine cyclobutane dimers is to be examined using a UV modified restriction fragment of phi X174 RFI as substrate. The two structural genes controlling the synthesis of the two correndonucleases are to be cloned and the numbers of gene copies to be amplified for potein structure determinations. The uvrC structural gene is to be cloned to facilitate isolations and characterizations of its gene product.